One of the basic technological goals when manufacturing analog resistors is to achieve a low dispersion or high stability control of the resistances across the analog resistors from die-to-die, wafer-to-wafer, and lot-to-lot.
Current methods to improve the cross-chip stability of analog resistors employ laser blowing, Zener diode “zapping”, or other techniques that generate a desired resistance. Such methods involve manufacturing resistor chains across a substantially large area of silicon and trimming the resistor chain to the desired resistance. The method of laser blowing creates open circuits in the resistor chain, while the Zener diode method creates short circuits within the resistor chain in order to achieve the desired resistances and thus cross-chip stability.
Such methodologies involve a substantial amount of processing time since they use the specific trimming and testing of each resistor chain across all dies in each wafer of every lot. The resistor chains also cover a large area of the silicon wafer, leading to a costly manufacturing process. For example, many of the resistors in the chain are not pertinent to the overall resistance, since most of the resistors are electrically disconnected using the various trimming techniques such as laser “blowing” or zener “zapping” as described above, and therefore significant areas of the wafer may ultimately be wasted.